WiFi: A Short Introduction to 802.11ax

Citation info:
Gautam Bhanage, "A Short Introduction to 802.11ax", Technical report GDB2018-001, published at bhanage.com, 2018

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802.11ax support for Uplink MU-MIMO

Who should read these?
At the time of writing this blog post the 802.11ax standard is in the process of getting ratified and we are at the version 2.0. Are you intrigued about what makes this standard different from the previous 802.11ac standard?

Download PDF of the TR.

Disclosure:
Slides from a talk I recently presented on 802.11ax technology.
These slides are purely based on my reading of the standards and other free documents available on the internet.
Copyright for the images are held by the owners. I have only used the ones which were labeled for reuse.

Tech report: GDB2018-001

Linux: Why use MSI over the GIC mechanism (Brief)

MSIs are implemented as a write from the device rasising the interrupt to a special memory location which causes raising of the MSI.

Two main reasons to consider MSI over PICs:

1. Speed: Pin based PCI interrupts are usually shared across devices and hence we would typically need to invoke each associated interrupt handler. MSIs are not shared so this does not arise.

Another case is that PCI can only support single interrupt per function. In this case drivers have to explicitly check what event happened (e.g. tx done, rx etc for a single MAC interrupt in case of Wifi radios). Using MSI, there could be a dedicated interrupt for each type of event (from the MAC).

2. Consistency: In case of pin based interrupts, the interrupt may be raised before the complete data has arrived in memory. There are ways to work around this. However, in case of MSIs this is not a concern since MSI writes cannot pass data writes on the bus.

Reference:
Linux Kernel Documentation - https://www.kernel.org/doc/Documentation/PCI/MSI-HOWTO.txt

WiFi: PER based adaptive AMSDU aggregation worth the effort?

This has been a lingering question. A lot of studies (including one of ours) in the past has delved into the support for AMSDU aggregation - and the ability to consider PER as a factor for adaptively controlling AMSDU aggregation. But is it worth the computational effort? Can this be simplified by making AMSDU aggregation static and using other mechanisms for limiting PER?

WiFi: Load balancing through probe response control

Basic Idea:

Clients use probe requests as one of the first frames before connecting to an access point (AP). If the AP does not respond with a probe-response frame, the client will not proceed with the connection. We leverage this condition to control how clients are distributed across multiple access points in the network. This approach to client - balancing has the advantage that:

1. Load both RF and CPU are balanced across the APs.

2. No disconnect/connect is required for load balancing.

3. Leverages the fact that typical WLAN mobility is pseudo-static. So clients will not move significantly from the places where they connect. Even in case of mobility, the disruption is minimal.

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Mixing MACs: An Introduction to Hybrid Radio Wireless Virtualization

Download Full PDF        |     ArXiv pub page

Abstract— This study presents the design of the hybrid wireless virtualization (HWV) controller based network architecture. Using a HWV controller, an unified approach can be taken for provisioning and management of virtualized heterogeneous radios, irrespective of their MAC and PHY layer mechanisms. It is shown that the airtime occupancy by transmissions from different slices or groups can be used as a single metric for tying these virtualized platforms. 

This paper discusses the architecture for doing a "network function virtualization" for wireless networks. An application for such virtualization of the radio architecture fits in directly with the neutral hosting concept being suggested in 5G wireless networks.